STEM study of the high-pressure oxidation of GeSi

Abstract

GeSi alloys are of interest because of their potential applications in optical and electronic devices. Understanding the growth of thermal oxide is very important for the GeSi system if an adaptationof the existing Si technology is going to be used. Thermal oxidation of GeSi leads to a Ge-rich layerat the GeSioxide interface. By sufficiently speeding up the rate of oxidation at a given temperature,such as with high pressure oxidation, it is possible to convert both Ge and Si into oxide and suppress the Ge pile-up at the oxide front. This was observed in the oxidation of GeSi films (Ge concentration 5-17 at.%) using pure oxygen at 600 atm and 550 °C. The segregation of Ge oxide from Si oxideand the Ge pile-up in high pressure oxidized GeSi, which are difficult to observe with other techniques, were studied by using a dedicated STEM.An epitaxially grown Si (2500 Å)/Ge.15Si.85 (500 Å) hetero-structure on Si(100) was oxidized in a wet ambient at 750 °C and 25 atm. It was then made into anXTEM (cross-sectional transmission electronmicroscope) sample and characterized using a VG HB 501A STEM equipped with EELS (electron energy lossspectrometry) and a windowless X-ray detector. STEM BF (bright field) and ADF (annular dark field) images are shown in Fig. 1(a) and 1(b). STEM BF images are similar to conventional TEM BF images. Fig. 1(a) shows that three layers of oxides are grown on the Sisubstrate.